Declaring variables after statements.

This is a discussion on Declaring variables after statements. within the C Programming forums, part of the General Programming Boards category; I have seen this done in some code samples and seen Salem saying that its not allowed in standard C. ...

  1. #1
    & the hat of GPL slaying Thantos's Avatar
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    Declaring variables after statements.

    I have seen this done in some code samples and seen Salem saying that its not allowed in standard C. What I was wondering is when is memory allocated and what the lifespan of the variable is when it is declared after statements.

    example:
    Code:
    int foo (void)
    {
    int blah, blah2;
    blah = something;
    switch (blah)
              {
              case 1:
                      blah2+=1;
                      break;
             case 2:
                     int blah3;
                     blah3=blah * blah;
                     break;
             case 3:
                     blah2=ok;
                     break;
            }
    return 0;
    }
    Could blah3 be used in case 3? case 1?

    I personally dont like it but I'd like to know how it works none the less.

  2. #2
    Registered User
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    In C you can't define variables after any statements. You can only do that in C++. You will get a compiler error in compiling that code.
    Depending on the version of the C++ compiler, earlier versions of compilers will have the scope of blah3 to be until the end of the function. Later versions, i think would have the scope end at the end of the switch statement.

  3. #3
    Been here, done that.
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    Re: Declaring variables after statements.

    In other words, your code is illegal because blah3 is not defined at a block beginning. This will work, though:

    Code:
    int foo (void)
    {
    int blah, blah2;
    blah = something;
    switch (blah)
              {
              case 1:
                      blah2+=1;
                      break;
             case 2:
                  {
                     int blah3;
                     blah3=blah * blah;
                     break;
                  }
             case 3:
                     blah2=ok;
                     break;
            }
    return 0;
    }
    In this case, blah3 is only available within the block defined.
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  4. #4
    Registered User Scribbler's Avatar
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    Sorry to necro this post, but another thread brought this topic to my attention...

    I was under the impression that you cannot declare variables after any statements in a function. However this code compiles and executes...
    Code:
    #include <stdio.h>
    
    int main()
    {
    	int input;
    	int x,y,z,zZ;
    
    	scanf("%d", &input);
    
    	x=y=input;
    	
    	int table[x][y];
    	int testVar = 0;
    
    	for (z=0; z < input ; z++)
    	{
    		for (zZ = 0; zZ < input ; zZ++ )
    		{
    			table[z][zZ] = zZ;
    		}
    	}
    	for (z=0; z < input ; z++)
    	{
    		for (zZ = 0; zZ < input ; zZ++ )
    		{
    			printf("%d",table[z][zZ] = zZ);
    		}
    		printf("\n");
    	}
    	printf ("%d\n",testVar);
    
    	return 0;
    }

  5. #5
    ATH0 quzah's Avatar
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    Quote Originally Posted by Scribbler
    Sorry to necro this post, but another thread brought this topic to my attention...

    I was under the impression that you cannot declare variables after any statements in a function. However this code compiles and executes...
    (Holy OLD THREAD, Batman!)

    That's because you can declare variables whenever you feel like it...

    ...in C99. Linky.

    Quzah.
    Hope is the first step on the road to disappointment.

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